High-speed printers are already known which upon receiving signals from a control unit print characters on a strip or sheet of paper, using the technique known as non-impact printing. Some of these machines include a flexible recording element comprising an endless ribbon or belt, on the surface of which sensitized zones, also known as latent images and corresponding to the characters or images that are to be printed, can be formed electrostatically or magnetically. These latent images are then developed, or in other words made visible, using a developer, which is typically in the form of a powdered product and is deposited onto the recording element. The developer remains applied only to the sensitized zones on this element so as to form an image in powder. After that, the recording element is put into contact with a print carrier, such as a sheet of paper, so that the particles of developer located on the sensitized zones can be transferred onto this print carrier, where it can be fixed definitively.
Printers of this type are described and shown in various patents, in particular in U.S. Pat. Nos. 3,076,393, 3,142,940, 3,161,544 and 3,254,626 and in French Patents No. 1 513 779 (corresponding to U.S. Pat. No. 3,495,268) and No. 2 209 322 (corresponding to U.S. Pat. No. 3,735,416). The flexible recording element with which these machines are equipped is mounted on rollers or pulleys which drive it along a closed path, along which it travels in succession past a device for recording the latent images, an applicator device which deposits particles of developer onto these latent images, a transfer device which effects the transfer of these developer particles onto a print carrier and finally an erasing device which assures the erasure of the images which have traveled past the transfer device.
Printers of this type can be classified essentially in two different categories. In a first category, including the printers described in the above-named U.S. Pat. Nos. 3,161,544 and 3,142,840, the print carrier, comprising a long strip of paper, remains continuously pressed against the flexible recording element. Given that in these machines of the first category this flexible recording element and this strip of paper are driven such that they are displaced simultaneously and continuously, at quite a high speed, that is, at least several tens of centimeters per second, then when they receive data that is to be printed and is sent to them virtually continuously by a control unit, these machines are capable of printing long strips of paper at a high printing rate, which in fact typically is in excess of 3000 lines of characters per minute. Nevertheless, it is not conceivable for these printers to be used for printing data that are sent intermittently by a control unit, because the strip of paper is driven uninterruptedly at the same rate as the flexible recording element, and so the quantity of paper traveling beneath the transfer device will be out of proportion to what is actually necessary to do this printing. Accordingly, in order to keep the quantity of paper needed for printing data sent intermittently by a control unit down to a reasonable amount, a second category of printers has been designed, which are described for example in the above-named U.S. Pat. No. 3,076,393 and in the above-named French Patents No. 1 513 779 and No. 2 209 322, in which the print carrier, which during its displacement traverses a transfer device in which it is located near the flexible recording element, is normally kept from being in contact with this element and is applied momentarily to it only when the portion of this element that is coated with developer particles intended for transfer onto the print carrier has arrived inside the transfer device. The momentary contact of the print carrier and the flexible recording elements is effected via a pressure plate, which under the control of a cam or electromagnet mechanism presses the print carrier against the recording element for a brief instant. The recording element rests on a plate or support element attached solidly to the printer. To assure that the developer particles that have been deposited on the flexible recording element will be transferred in their entirety onto the print carrier, and that this transfer will be made with all the care needed for obtaining high-quality printing, it is absolutely necessary not only for this carrier and this element to be completely immobilized at the moment when they are put into contact with each other, but also for the pressure plate to be mounted such that it will not vibrate at the moment when it assures the placement of the print carrier in contact with the recording element. To accomplish this result, these printers of the second category must therefore be provided, first, with clutch and brake devices of sufficient capacity that they can communicate rapid accelerations and decelerations to the recording element and, second, with damping devices capable of very rapidly damping the vibrations generated by the repeated impacts of the pressure plate against the support plate. Furthermore, these printers require that the register marks be recorded on the recording element. When the marks pass close by a detection device, the marks are read to cause the braking and then the immobilization of the recording element at the precise moment when the data that are to be printed and are recorded on them arrive at the level of the transfer device. In addition, in the case where the flexible recording element is fabricated from a very thin metal tape, which after being flexed has its two ends joined and then soldered in order to produce an endless tape, it is absolutely necessary to provide this machine with a detection device which causes the recording of data onto the tape to be stopped during the entire time while this soldered zone travels past the recording device. Experience teaches that in this soldered zone, it is virtually impossible to form latent images for characters in which the contours are perfectly well defined. As a result, in the final analysis these printers print the data at a lower speed than the printers in the first category and prove to be complicated and expensive.
Although it has been possible to meet most of the above requirements, still there has been no success in eliminating the vibrations which arise in the flexible recording element either because of the repeated impacts of the pressure plate against the support plate or because of the shock-like displacement of this recording element. Under these conditions it is very difficult to obtain high-quality printing. In addition, the recording element in these machines, which is driven intermittently, is subjected to considerable friction, during the forceful accelerations and decelerations, caused by the pulleys or rollers on which it is mounted. There is very rapid wear as a result, which during normal machine operation requires the operator to replace this recording element quite often, in fact virtually every other day.